1. Field of the Invention
In the context of the preferred and modified embodiments chosen for illustrating the invention, it relates to improved apparatus for concurrently effecting controlled separate electrical connections to a permissably numerous plurality of permissably densely arranged contact points, such for example as the multitudinous contact structures representing test points on an electronic printed circuit board to be tested (all of which typically must be contacted simultaneously during testing), and for doing so in manner which also facilitates electrically coupling each of such connections with the corresponding terminals of circuit testing equipment or the like.
In a somewhat broader context, the invention is concerned with providing improved means employing a preferably resilient, flexible diaphragm and a fluid pressure differential for simultaneously, but independently, urging a plurality of rigid, pin-like contacting elements into respective engagement with a corresponding plurality of contactable structures with substantially equal forces, thereby also effecting separate electrical connections with each of such structures when such elements are formed of electrically conductive material and such diaphragm is formed of electrically non-conductive material.
Thus, in terms of the applications for which the embodiments of the invention described herein for illustrative purposes were developed, the field of the invention is the art of electrical interconnect systems employed for the testing of single or multilayer, printed circuit boards or the like, with particular emphasis upon the effectuation of electrical connections between the electrical terminals of the "wiring or circuit analyzer" or other testing equipment and the electrical test point terminals of the units to be tested. Those skilled in the electrical and mechanical arts should recognize, however, that the principles and the structural and functional aspects of the invention may also have significant utility in diverse other applications involving the effectuation of substantially equally forceful, separate, respective engagements with a plurality of individually contactable structures, for purposes of effecting independent electrical connections with the latter or otherwise, especially whenever the zones of engagement are numerous or closely spaced or when it is desirable for economic, reliability or other reasons to effect such engagements through simple rigid pins rather than spring-biased compressible elements.
2. Description of the Prior Art
The electrical testing of printed circuit boards and similar electronic modules in commercial quantities is typically carried out with the use of circuit testing equipment which may be controlled or programmed to sequentially apply appropriate energizing signals to various electrical contact structures or test points on the units to be tested, to sense the resulting electrical parameters between those or at other of such test points, and to detect and indicate or record any faults in the characteristics of the various portions of the internal circuitry of the tested units (e.g., open circuit paths, short circuits, unintended leakage paths or other static or dynamic conditions). Since a number of similar units are normally to be successively tested, it is necessary to provide some means for quickly and conveniently effecting and releasing electrical connections between the terminals of the testing equipment and the appropriately related test points of each of the successive units to be tested, that matter being complicated by the normally multi-terminal nature of both (hundreds or even thousands of terminals being typical) and the fact that the test points on the units to be tested will typically be arranged in a relatively dense and more or less arbitrary pattern.
Conventional prior practice in effecting such electrical connections between the terminals of the circuit testing equipment and the test point contact structures of a succession of printed circuit boards or the like of a given type to be tested has been to provide a fixture for successively receiving the units to be tested, with the unique pattern of test points of the latter in spaced, facing relationship to an array of contacts respectively electrically connected with the terminals of the testing equipment and relatively movable with respect to the unit to be tested for effectuation of electrical connections with each of the test points of the unit under test in one of the ways next described.
In applications in which a given piece of testing equipment and the associated fixture may economically be dedicated to the testing of very large quantities of identical printed circuit boards or the like on a continuing or relatively long term basis, it may be feasible to arrange the array of contacts provided by the fixture and associated with the terminals of the testing equipment in the same unique pattern as the locations of the test points on the units to be tested to permit making connections therebetween responsive to relative movement of such contacts of the fixture and the unit under test toward each other. Even in those instances, however, it has normally been found necessary to effect such connections between the contacts associated with the terminals of the testing equipment and the test points on the unit under test by means of electrically conductive, springbiased, compressible connection pins, which may be either utilized as the contacts associated with the terminals of the testing equipment and more or less permanently wired to or otherwise coupled with the latter or by employing such spring-biased pins intermediately between the contacts associated with the testing equipment and the test points of the unit under test. In the latter type of arrangement, the intermediately disposed, spring-biased, connection pins typically would be supported by an apertured plate or the like having pin receiving holes aligned along the axes extending between each contact associated with the testing equipment and a corresponding test point on the unit to be tested.
In what is believed to constitute the majority of practical applications for such circuit testing arrangements, however, there will be only a more limited number of printed circuit boards or the like of each of a continuing variety of types to be tested over relatively shorter periods so that it is economically impractical to exclusively dedicate a given piece of circuit testing equipment to the testing of only a single type of printed circuit board or the like; and it is, therefore, not feasible to provide merely a single fixture and interfacing arrangement of the type last described with any given piece of circuit testing equipment. In fact, it is commonly required that a given piece of circuit testing equipment may be employed for testing different specific types of printed circuit boards or the like from time to time as commercial circumstances may demand. Effort has been made to cope with the last-mentioned problem by providing the fixture with a "standard" array of contacts which are more or less permanently coupled with the respective terminals of the testing equipment and which are arranged in a regular grid or matrix pattern with the contacts on uniformly spaced Cartesian coordinates typically 1/10 inch apart, and employing therewith a plurality of differing types of electrical interfacing assemblies, often called "transition boxes" , with a differently arranged interfacing box being required with each type of printed circuit board or the like to be tested in order to provide contacting structures properly aligned with the typically irregularly patterned arrangement of test points on each particular type of units to be tested. Such boxes must electrically interface on one side thereof with the regularly arranged contacts of the matrix associated with the terminals of the testing equipment, while electrically interfacing on the opposite side thereof with the irregularly arranged pattern of test points on the particular type of units in whose testing such boxes are to be respectively employed; this dual and opposite interfacing essentially accomplishes a coordinate transformation between the contacts of the permanent matrix and the unique patterns of test points of the particular type of unit to be tested for which the board was designed. Since such interfacing assemblies must provide for effecting electrical connections between contacts associated with the testing equipment and logically corresponding test points on the unit to be tested which may be laterally offset with respect to such contacts, there have been a substantial variety of constructions proposed or employed for fabricating such transition boxes. By virtue of the common employment of fixtures depending upon relative movement between the array of contacts associated with the testing equipment and the unit under test, which are usually disposed in physical opposition to each other, in order to effectuate the required electrical connections therebetween, as well as the known tendency of some contacts in arrays thereof to significantly deviate from precise co-planarity with others, however, such interfacing assemblies have predictably heretofore utilized spring-biased, compressible, electrically conductive, intermediate connecting pins for effecting engagement type connections with the contacts associated with the testing equipment, the test points of the unit under test or both. In a typical transition box, one set of spring pins faces the array of contacts associated with the testing equipment, another set of spring pins oppositely faces the test points of the unit under test, and corresponding pins of such oppositely facing sets are hand wired together therebetween.
Experience in utilizing various types of the sort of conventional arrangements heretofore available, however, has revealed various shortcomings and limitations thereof. Many of the disadvantages of such prior arrangements are largely traceable to what has previously been the apparent necessity for using spring-biased, compressible type connecting pins, as well as the assumption that the transition box should be deployed between the contact array associated with the testing equipment and the test points of a physically opposed unit to be tested. Because of their relatively small size and the nature of their construction, such spring-biased connection pins are quite expensive, as is the task of providing hand-wired jumpering between oppositely facing sets thereof.
The overall problem is compounded by the substantial number of spring-biased pins required in each conventional transition box, the attendant statistical probability of failure of at least a few spring-biased pins in any given box after substantial use of the latter, the fact that such an interfacing assembly can no longer be used after failure of even a single spring-biased pin without adversely affecting the testing being performed or possibly damaging the unit being tested, and the difficulty, time and expense in attempting to replace defective spring-biased pins and their jumpering connections in an interfacing assembly requiring a great number of such pins in closely spaced relationship. The assumption that transition boxes must be physically disposed between the contact array associated with the testing equipment and the unit under test and, therefore, employ oppositely facing sets of connector pins, has led to further unnecessary expense and inconvenience in the design, fabrication and utilization of fixtures and interfacing assemblies for the mentioned purpose, and has incidentally resulted in failure of prior apparatus of such general class to effectively take advantage of the cost and other advantages of the technique of so-called "wirewrap" connection of electrically conductive leads, which is now in such common use in many other areas of electrical apparatus. The regretable fact of the matter is that proper testing of many types of relatively low quantity printed circuit modules and the like is simply foregone due to the objectionably high cost of fabricating conventional transition boxes for testing such units.
Another disadvantage of using spring-biased, compressible connector pins is that, although they do provide compliance for compensating to some extent for lack of co-planarity between the various contacts to be engaged, they do so in a non-linear fashion dependent upon the amount of compression induced by the "height" of each individual contact, which results in differing forces of individual contacting engagement with the various contacts. At the level of forces typically employed in such applications, the engagement with some contacts may be inadequate for optimum electrical connections being effected, and, if all of the spring strengths are increased to avoid that, their aggregate forces may damage units being tested.